The present invention generally relates to recording and reproducing apparatuses for recording and reproducing video signals on and from a magnetic tape whose traveling speed can be selectably changed. More particularly, the present invention relates to a video signal recording and reproducing apparatus having a circuit construction capable of easily performing preset correction of tracking at few adjusting positions, in an apparatus for recording and reproducing video signals on and from a magnetic tape of a given length which is traveling at a tape speed in accordance with a mode selected from between a long-time (long-duration) recording and reproducing mode and a short-time (short-duration), that is, regular recording and reproducing mode.
Generally, in video signal recording and reproducing apparatuses, an audio signal accompanying the video signal is recorded and reproduced by a stationary head. Hence, as the traveling speed of the magnetic tape is increased, the recording and reproducing characteristics and the signal-to-noise (S/N) ratio of the audio signal are improved. In addition, undesirable effects such as noise due to wow and flutter of the magnetic tape becomes relatively small. On the other hand, as the traveling speed of the magnetic tape is increased, the recording and reproducing time for a given length of magnetic tape becomes shorter.
Accordingly, a video signal recording and reproducing apparatus which can be selectively operated, according to the purpose of use, in a short-time recording and reproducing mode having a high magnetic tape traveling speed and a long-time recording and reproducing mode having a low magnetic tape traveling speed, has been reduced to practice in a concrete form. Since recording and reproduction are carried out with the tape driven at a high speed in the short-time recording and reproducing mode, the recording and reproducing time is short for the same tape length, but the audio signal is recorded and reproduced with good characteristics. In the long-time recording and reproducing mode, although the characteristics of the audio signal are somewhat inferior to those in the case of the short-time or regular recording and reproducing mode, recording and reproduction of the video signal and the audio signal for an even longer period can be carried out.
In a video signal recording and reproducing apparatus of this heretofore known kind, however, the track width of the magnetic head, the traveling speed of the magnetic tape, and the like are set so that the tracks are formed without gaps therebetween in the long-time recording and reproducing mode. For this reason, in the short-time recording and reproducing mode, gaps are formed between adjacent tracks, whereby guard bands are substantially formed, as described more fully hereinafter in conjunction with a drawing. As a disadvantageous consequence, the tape utilization efficiency during this short-time recording and reproducing mode has been poor.
Accordingly, a video signal recording and reproducing apparatus in which the above described disadvantages have been eliminated, was proposed in a U.S. Pat. No. 4,293,880 in which the assignee is the same as that of the present application, and reduced to practice. This proposed video signal recording and reproducing apparatus is provided with a first pair of magnetic heads having a certain track width for long-time recording and reproduction, and a second pair of magnetic heads having a track width greater than the above certain track width for short-time or regular recording and reproduction. These pairs of magnetic heads are selectively used by switching according to the recording and reproducing mode. According to this proposed apparatus, the tracks are formed without gaps, and the tape utilization efficiency is high, not only during the long-time recording and reproducing mode (hereinafter simply referred to as long-time mode), but also during the regular recording and reproducing mode (hereinafter simply referred to as regular mode). Particularly during the regular mode, portions heretofore left as gaps on the magnetic tape are also used for the recording and reproduction. This enables recording and reproduction with high S/N ratio, and further, reduces the generation of dropout.
The apparatus reduced to practice, can be switched between a 2-hour regular mode and a 6-hour long-time mode, with respect to a standard type cassette tape. Speaking in more concrete terms, the apparatus has a rotary body provided with a first pair of video heads for 2-hour recording and reproduction, and a second pair of video heads for 6-hour recording and reproduction. During the 6-hour recording and reproducing mode, the tape is caused to travel at a speed which is 1/3 the tape traveling speed upon the 2-hour recording and reproducing mode. In addition, the track width of the second pair of video heads is selected to 1/3 the track width of the first pair of video heads.
Generally, in this kind of so-called helical scan type recording and reproducing apparatus which records and reproduces the video signal on and from tracks formed obliquely with respect to the longitudinal direction of the magnetic tape by rotary video heads, it must be possible to finely reproduce a magnetic tape recorded by one recording and reproducing apparatus by another recording and reproducing apparatus. That is, the video heads of the latter apparatus must positively and accurately scan over the tracks on the magnetic tape recorded by the former apparatus. Accordingly, a distance L along the tape traveling path between a position where the scanning of the track on the tape by the video head is terminated, and a position where a control head for recording and reproducing a control signal on and from an end edge of the tape makes contact with the tape, is determined according to a standard. Thus, in order to set the distance between the above two positions to the predetermined distance L, the following adjustment was conventionally performed. That is, the control head is mechanically mounted at a position where the above distance becomes substantially equal to the predetermined distance L. Next, a frequency-modulated signal is recorded onto the magnetic tape by the rotary heads while a control pulse is recorded onto the tape by the control head. Then, these signals thus recorded onto the tape are reproduced by the same recording and reproducing apparatus, and the time constant of a monostable multivibrator in a reference signal generating circuit part within a capstan servo circuit, for example, is adjusted so that the level of the reproduced frequency-modulated signal becomes maximum. Thereafter, a standard tape pre-recorded in an ideal state by a magnetic recording and reproducing apparatus having the predetermined distance L is reproduced, and the position of the above control head is adjusted so that the level of the frequency-modulated signal reproduced from the standard tape becomes maximum.
However, even in the above recording and reproducing apparatus which selectively operates in the regular mode and the long-time mode with the video heads exclusively for each mode, only one control head is provided. Thus, the condition with respect to the above distance L must be satisfied in both the regular and long-time modes. But irregularities to some extent inevitably exist in the tape driving system in the regular and long-time modes, positional adjustment of the control head, and relative height positions of the first pair of video heads and the second pair of video heads. Therefore, if the distance L is adjusted by mechanically positioning the control head during the regular mode, the value of the distance L becomes different during the long-time mode. This introduces problems in the tape interchangeability.
Moreover, in the above recording and reproducing apparatus, the adjustment of the distance L with respect to the regular mode (or the long-time mode) can be performed by mechanically adjusting the position of the control head, but the position of the control head cannot be adjusted mechanically in the long-time mode (or the regular mode). Thus, measures were taken by electrically compensating for the deviation of the actual distance L from the predetermined distance L in the long-time mode (or the regular mode), so that the actual distance L and the predetermined distance L become equivalent on the magnetic tape.
However, the tracking adjusting operation to accurately obtain the above predetermined distance L and achieve normal tracking, is exceedingly complex and troublesome. In the conventional apparatus, for example, it was necessary to perform four adjusting steps.